Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$78.32	13.446%	$88.8509	$88.85	$88.85	$88.90
Purchase #2	$141.69	9.189%	$154.7099	$154.71	$154.70	$154.70
Purchase #3	$245.40	10.602%	$271.4173	$271.42	$271.40	$271.40
Purchase #4	$112.88	13.817%	$128.4766	$128.48	$128.50	$128.50
Purchase #5	$246.45	4.443%	$257.3998	$257.40	$257.40	$257.40
Purchase #6	$22.76	3.394%	$23.5325	$23.53	$23.55	$23.50
Purchase #7	$229.33	9.216%	$250.4651	$250.47	$250.45	$250.50
7 purchase totals =	$1,076.83		$1,174.8521	$1,174.86	$1,174.85	$1,174.90